Collection chamber for making mats of inorganic fibers

ABSTRACT

A collection chamber located between a source of gas entrained inorganic fibers and a collection surface upon which mats of the fibers are formed. The side walls of the chamber in various configurations enhance the mixing of cooling gas, binder and the entrained fibers while reducing turbulence and enhancing control of fiber deposition. Divergent side walls above the collection surface diffuse the binder coated fiber and reduce its velocity so that it is deposited in a blanket of uniform density and thickness across the collection surface. Convergent side walls from a region adjacent the fiber source reduce turbulence and back flow in this region while facilitating the mixing of cooling air with the hot fiber entraining, high velocity blast, and the distribution of binder in the mixed fiber-gas stream. A collection chamber having walls of the general form of a hyperbola is disclosed with given height, width of collection surface, throat dimensions and throat location relationships for superior results. Compromise collection chamber forms to accommodate plant and equipment restrictions are discussed.

l ll 3,787,194

[4 1 Jan. 22, 1974 United States Patent [191 Rayle et al.

ABSTRACT COLLECTION CHAMBER FOR MAKING MATS OF INORGANIC FIBERS A collection chamber located between a source of gas entrained inorganic fibers and a collection surface mwd wm ma kn w m k mflm WG r m am mks J n n m .mm B M m m n e v I upon which mats of the fibers are formed. The side Ind.

[73] Assignee: Johns-Manville Corporation,

walls of the chamber in various configurations enhance the mixing of cooling gas, binder and the entrained fibers while reducing turbulence and enhanc- Greenwood Village, Arapahoe County, Colo.

May 16, 1972 Appl. No.: 253,708

ing control of fiber deposition. Divergent side walls above the collection surface difiuse the binder coated [22 Filed:

fiber and reduce its velocity so that it is deposited in a blanket of uniform density and thickness across the collection surface. Convergent side walls from a region adjacent the fiber source reduce turbulence and 1. 2mmm 57/ M234 4 6 2 2 3 oo mm mw n 7 5 9 64 my 9 m n0 5 3 6 moo m0 "8 u 5 2 .c u "r u a n u L I 0 m d S Ld U mm H UN 5 55 .I. [l

[56] References Cited height, width of collection surface, throat dimensions and throat location relationships for superior results.

Compromise collection chamber forms to accommodate plant and equipment restrictions are discussed.

S T E.- T 1 mum mm Aha The SRR D wm n99 NHH UUH 68 69 mm 22 Underwood Primary Examiner--Robert L. Lindsay, Jr. 8 Claims, 5 Drawing Figures Attorney, Agent, or Firm-John A. McKinney et al.

PATEHTEU JAN 2? 19/4 SHEET 1 BF 2 FI6.I

PATENTEI] JAN 2 2 H174 SNEEI 2 [If 2 FIG. 2

FIG. 4

COLLECTION CHAMBER FOR MAG MATS OlF INORGANIC 1F HBERS CROSS REFERENCE TO RELATED APPLICATIONS One form of collection chamber having shaped side walls and superior operating charcteristics by virtue of self cleaning features is disclosed in the patent application of Harvell M. Smith and Robert E. Hengstler filed herewith entitled Continuously Cleanable Collection System, Ser. No. 253,841 filed May 16, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to apparatus for forming mats or blankets of inorganic fibers and more particularly to collection chambers having shaped walls.

2. Description of the Prior Art: Heretofore it has been common to enclose the flight path of fibers between a fiber former and the point of fiber collection. Such enclosures, termed collection chambers usually are rectangular in plan and have planar walls. When the fiber formers are directed vertically so that fiber is issued vertically downward toward a fiber collection surface at the bottom of the box-shaped enclosure, the fluid flow results in high turbulence and a high degree of randomness in the resulting felt of fibers collected.

It is highly desirable that the fluid, comprising fibers entrained in a high velocity gas stream, for example air and combustion products at the melting temperature of the fibers to enable them to be attenuated, be slowed and cooled. This slowing facilitates collection of the fibers without passing them through the foraminous surface of the collection surface. The cooling permits a thermosetting binder to be distributed over the fibers without advancing its cure excessively prior to further processing of the fiber blanket. While binders in powder form are employed, they frequently are applied as an aqueous solution or suspension in a spray or mist whereby the liquid further cools the primary blast. Thus prior practices have sought to mix finely divided binder into the gas-fiber stream.

Boundary layer effects including separation turbulence are present in systems of the above nature due to the differences in the velocities at which the constituents are introduced. That is, the high velocity fiber and gas stream encounters the slow cooling gas stream to produce boundry layers and the intermediate velocity binder stream introduces another source of boundry layer effects. Turbulence occurs due to the boundry layer effects as augmented by the turbulence inherent in the fiber attenuating gas blast so that fiber and binder can recirculate with the hot gases to build up the temperature in the collection chamber and at least partially cure the binder even while in the chamber and above the collection surface.

The fluid flow in collection chambers is subject to the Condeia Effect such that the stream tends to follow a confining surface and be subject to major shifts in flow patterns in response to minor transverse flow disturbances in the manner of an amplifying fluidic switch. Such stream concentrations and shifts result in localized regions of greater fiber density or thickness of buildup on the collecting surface which are detrimental to the efficient production of fiber mat of uniform density.

Eddys and the turbulence in the main flow of the mixture requires extra horsepower to achieve the necessary air flow developed as a suction behind the foraminous collection surface. Further, the eddys and turbulence cause the binder and fiber to impinge upon the collection chamber walls and adhere thereto. Such adherence and the temperature buildup due to recirculation in the collection chamber results in an accumulation of partially or fully cured binder on the walls. Accumulations of the order of a foot in thickness are experienced with an attendant reduction in efficiency of the process due to the reduced chamber volume, reduced width of collected mat, and reduced mat quality attributed to the debris which randomly falls from the walls onto the collection surface. As a result, frequent interruptions in production are required to clean the walls of the collection chamber.

SUMMARY OF THE INVENTION The present invention militates against the above problems by control of the fluid flow through a collection chamber by means of shaped chamber walls. In one form the side walls are shaped] so that a cross section of the chamber is of the general form of a hyperbola having its axis extend from the fiber forming or introduction region to the transverse center of the fiber collecting surface. Such a form of sidewall in its converging section minimizes turbulence, eddys and back flow in the regions subject to boundry layer effects while permitting the cooling gas to cool the hot blast, slowing the hot blast while accelerating the cooling gas, and distributing the binder to form a generally homogenous stream of fiber, binder and gas. In the diverging section of the chamber sidewalls the binder coated fibers are dispersed in a stable pattern with improved uniformity of distribution on the collection surface. Thus the shaped walls enhance the combination of gas fiber blast with cooling gas and binder, increase the efficiency of air flow, reduce suction horsepower requirements, reduce eddy currents, reduce buildup on the chamber walls, stabilize gas flow patterns, distribute the weight of fibers of the felt more uniformly across the width of the collection surface, and stabilize the weight distribution of fibers on the collection surface.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic perspective of a forming chamber according to this invention and includes portions of typical fiber formers and a fiber collection means to illustrate the general organization of the elements;

FIG. 2 is a cross-sectional view of FIG. 1 taken along line 22 of FIG. 11; and

FIGS. 3, 4 and 5 are modified forms of collection chamber viewed as in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings illustrate various forms of chambers adapted for the collection of particulates entrained in a gas stream directed toward a collecting surface. One particular utilization of such combinations is for the collection of mineral fibers derived by forcing molten material through apertures to form primary fibers which are then attenuated to finer secondary or staple fibers by a high velocity, high energy gas blast which entrains the secondary fibers.

Mat is produced from secondary fibers by melting the mineral for example fiberizable glass, in a glass furnace having a forehearth which delivers the molten glass to fiber formers 11 (all by means not shown). In the illus' tration five aligned fibers formers 11a through He are shown aligned along the longitudinal center plane of the collection chamber 12 with their centerlines evenly spaced from each other and the collection chamber end walls 13 and 14 at a uniform height above a collection surface generally referred to as 15. Each fiber former 11 comprises a motor driven basket 17 rotating in a horizontal plane around a vertical shaft 18 at speeds which cause glass delivered to the bottom of the basket by a duct (not shown) from the forehearth to flow as a thin molten sheet to the basket periphery. The upward extending side walls 21 of the basket 17 are perforated with an array of holes through which the molten glass is extruded under the influence of centrifugal force as primary filaments 22.

The plurality of centrifugally extruded primary filaments 22 from each basket 17 intercept an annular stream of high velocity, high energy gas which is directed vertically downward. Such a stream is derived from the annular orifice (not shown) of an attenuating burner 23. The resultant annular stream of gas reduces the pressure within the region it encloses by virtue of the Venturi effect of its flow so that the fibers tend to be turned inward toward a projection of the rotating axis of the fiber forming disc or basket 17 after they are attenuated by the acceleration imparted to their leading portions as they progressively are exposed to the attenuating gas blast.

The shroud of attenuated fiber and hot gases is advanced toward the collecting surface and binder is applied as a spray or mist from spray heads 24 in communication with an annular binder header 26. The binder is conventionally a water suspension of a thermosetting resin. It is desirable that the binder thoroughly coat the fibers so that they can be bonded into a loosely felted mat having sufficient integrity for further handling. Bonding and the curing of the binder should occur only after the fibers have been collected on the collecting surface 15. This dictates the cooling of the fibers while in flight to a degree which will not cause appreciable precure of the binder on the fibers in flight and on the collecting surface.

Normally the glass fibers are collected on the upper surface of a foraminous flight 15 of a horizontal conveyor which can be a continuous loop screen or chain having a head pully 27, a tail pully 28 and an underlying support grid 29 for maintaining the conveyor and accumulated fiber over a suction box 31.

Fiber will enter the open surface of the collector 15 as a function of its velocity and accordingly the gas blast and entrained fibers should be slowed so that fiber penetration of the flight is minimized and the mat collected thereon can be separated therefrom with minimum fiber loss through its retention in the flight.

The collection chamber 12 encloses the flight of the fiber from the fiber formers l l to the collection surface 15. Collection chamber form influences fiber flight as it progresses from primary streams 32 made up of the attenuated fibers from a fiber former and the hot gas from the attenuation burner 23 to merge with the secondary stream of ambient air introduced at the top of the chamber 12 between the burner 23 and the margins of the chamber walls. Control of the binder stream 34 from spray heads 24 is also accomplished in the collection chamber 12 to distribute that binder through the fiber.

Boundary layer effects are present where the high velocity hot gas-fiber stream 32 interfaces with the inspirated and suction induced low velocity ambient air stream 33 and where the intermediate velocity binder stream 34 is introduced in both the high velocity stream and the low velocity ambient air. if the streams are laminar, and in practice they at most only approach this condition, these velocity variations result in velocity gradients which are related to the distance from their interfaces. Shear develops between the lamina and ideally laminar flow results in no transfer of fluid masses between adjacent layers.

In practice the streams from the fiber former, the attenuation burner, the ambient, and the binder nozzels are not introduced with pure laminar flow. The turbulent flow involves secondary irregular motions and velocity fluctuations superimposed on the main or average flow. This flow occurs particularly at the interfaces between the streams. Some turbulence is desirable provided it can be controlled. That is it facilitates the mixing, in the case of the fiber-hot gas stream and ambient air to cool the fibers. In the case of the at least partially cooled fibers and binder spray some turbulence enhances the distribution of the binder over the fibers. Control of this mixing is desired for purposes of avoiding the spurious flow of binder or fibers as back flow out of the collecting chamber or impingement upon the collecting chamber walls. Turbulent flow should also be limited since it involves energy losses which must be made up by power input to the suction fans (not shown) of the suction box 31 below the collection conveyor 15. Shear stress in turbulent flow includes a factor of dynamic viscosity, variously called exchange coefficient and eddy viscosity, which contributes to the detrimental power losses.

l-leretofore it has been common practice to arrange collecting chambers 12 which had downwardly directed fiber formers 1 1 and fiber collection surfaces 15 at their bottoms with vertical side and end walls. Such chambers relied upon stream inspiration of ambient air, the negative pressure gradient to the foranimous collection surfaces and gravity to direct the flow of mixed binder, fiber and cooling air to the collection surfaces without spurious fiber flow. In some instances the upper portion of the side walls of collecting chambers have been inclined inward from the lower vertical wall portions, i.e., they have diverged from the fiber former, in an effort to enhance the flow by checking back flow. Studies of these configurations reveal that a significant amount of recirculation of the flow occurs within the chamber and that eddys develop in the vicinity of the diverging sidewalls.

Prior fiber collection chambers have exhibited a tendency to concentrate fiber flight along a side wall. This tendency is attributed to the Condiea effect. The skewing of the fiber flight results in a greater density or thickness of fiber blanket deposit on one side of the collection surface 15 such that as the blanket is advanced from beneath the seal roll 36 at the exit end of the advancing collection surface 15 the blanket has an irregular contour. Since product quality is determined by the minimum density across the blanket width, these variations require the incorporation of material in excess of that required in the balance of the blanket width with a consequent increase in product cost.

Skewed fiber flow is quite unstable. It is responsive to external influences of a minor nature in the manner of a fluidic switch. Flow shifts from along one side wall to along the opposite wall in response to changes in the vicinity of the apparatus such as a draft of air or a minor disruption in the flow of inspirated air intermediate the fiber formers 11 and the walls of the chamber 12.

According to this invention the mixing of the binder, fiber and cooling air is enhanced, the backflow of fiber is avoided, the fiber flight is centered and stabilized, the fiber buildup on the sidewall is reduced, and a suitable distribution of fiber on the collection surface is achieved by a collecting chamber 12 in which the side walls are shaped in vertical cross section with an upper convergent section 37 and a lower divergent section 38. A preferred form for such side walls is generally that of a hyperbola wherein the upper converging section center the stream on the center longitudinal plane of the collection chamber and resists the tendency of the stream to follow a sidewall of the chamber. The converging section also causes the binder, fiber and cooling air to mix. The lower, diverging section diffuses the mixed and cooled binder-fiber air suspended flow and slows it to lay down a layer of fiber of more uniform density and thickness across the collection surface than attainable heretofore.

Prior efforts to center the fiber flow to the collection surface have involved the placement of stream deflecting devices in the chamber particularly in the vicinity of the fiber formers 11 and burners 23. Where some success has been achieved the resultant blanket 39 of fiber as collected on surface 15 tends to have a greater thickness in the center of its cross section than at its sides. It has been found that the divergent section 38 enables the cross section contour of the blanket to be controlled according to the suction imposed from chamber 31 whereby variations can be achieved from the prior centered hump to an essentially level condition and, at high suctions, to even a dip in the thickness at the cross section center.

It has been found that the form of the walls of the collection chamber 12 can be related to the dimensions of the collecting surface 15. Chamber side walls 39 are shown supported by struts 41 extending from a vertical base frame 42 mounted on a support structure 43 defining the walls of suction chamber 31. Where conventional suctions are imposed from suction chamber 31, optimum results are achieved with the perforated walls 21 of the fiber former rotating basket 17 a distance above the collecting surface 15 of about 360 percent of the width of 15 and the upper limit of the side walls 39 a distance above 15 about 330 percent of the width of 15. As shown in FIGS. 1 and 2, optimum flow control is achieved when the width of the side walls 39 is effective from a position approaching an asymptotic relationship to the horizontal as at 44 so that the outer limits of the opposed walls are spaced about 300 percent of the width of collection surface 15. A smooth curve is defined by each side wall 39 to a throat section 45 which has a width about 45 percent of the width of the collection surface 15 and is located above the collection surface a height of about I50 percent of the width of 15. Side walls 39 diverge from throat region 45 to the collection surface 15 and approach that surface at a substantial angle to the surface.

The flared mouth 46 of the collection chamber 12 provides flow paths for ambient air which approach the horizontal as an asymptote in a generally hyperbolic form and are spaced from the fiber fonners l1 and attenuation burners 23 so that the flow paths are essentially unobstructed by either those elements or their supporting and feeding structures. The mixed and centered stream passes through the throat region 45 and that composite stream is slowed and dispersed in the divergent section 38. The smooth gradually flaring surfaces of section 38 minimize eddies as the binder coated fibers are carried to the collection surface 15.

Flow of gas to the suction chamber 31 varies along the length of collection surface 15 from a relatively unimpeded, high rate of flow at the up stream end of surface 15 to a relatively low rate of flow through the fiber pack collected on the surface as it advances to the exit at seal roll 36. As a result of this variation a wide range of Reynolds numbers are experienced at the collection surface. This will be appreciated when it is recognized that while the volume of gas drawn through surface 15 is about times the volume of the primary jets the rate of fiow of that gas and thus its temperature, viscosity and velocity vary with the amount of fiber on the surface 15 from an essentially fiber free surface at the up stream end to a full pack at the down stream end. The dimensionless Reynolds numbers are a function of the density of the fluid, the average velocity of the fluid, and the viscosity of the fluid.

The parameters of the collection chamber of FIGS. 1 and 2 as noted above were developed for broad range of Reynolds numbers. This enabled the side wall configuration to be established for the length of chamber 12.

In practice, plant layout and the associated equipment and supporting structures dictate against the ide alized flared mouth 46 defined by walls which are asymptotic to the horizontal as shown in FIGS. 1 and 2. Much of the benefits of those configurations can be realized by a compromise in the form of the convergent region 37 wherein the mouth 47 has a width generally equal to the width of the collection surface 15 as shown in FIG. 3. The divergent section 38 can be of the same proportions as for FIGS. 1 and 2 that is, a throat height of about percent of the width of surface 15 above collection surface '15 of a throat width of about 45 per cent of the width of 15 with a smooth flare in the walls from throat to collection surface. The distribution of the stream and the reduction of its velocity is effectively achieved in the divergent section of FIG. 3 while the modified convergent section retains the benefits of cooling the fiber by introduction of ambient air and the water'binder mist without backflow. It also centers the stream and stabilizes it. Eddies and boundary layer effects are reduced from that experienced in straight wall chambers by the convergent walls of FIG. 3 although it is to be appreciated that a greater amount of fiber impinges upon and adheres to the walls than in the optimized form of FIGS. 1 and 2. This is attributed to the reduced opportunity to develop stream lines conforming to the chamber walls.

In FIG. 4 only the divergent section 38 is employed. The upper sections of the collecting chamber walls are planar and parallel at 48 so that some loss of control of fiber flow is experienced over that achieved with the walls of FIGS. 2 and 3. Further, a greater suction must be maintained to avoid loss of fibers through back flow and eddy effects near the entrance to the chamber. The straight walls tend to accumulate fiber more rapidly than in the case of the convergent walls and thus require more cleaning down time than for the embodiments described above. Further, the fibers impinge upon the foraminous collecting surface 15 at higher ve locities than for the embodiments where a lower suction is utilized in the suction box, and as a result, a greater fiber carryover by the collection surface 15 occurs when the blanket is separated from the surface. Without the convergent section, the less effective fiber directing means of the prior art are employed to minimize and control the tendency of the stream to follow a side wall.

One practical compromise of the convergentdivergent collection chamber sidewall form is shown in FIG. 5 wherein planar convergent walls 51 define the convergent section 37 and planar divergent walls 52 define the divergent section 38. In a structure of the form illustrated the throat width and location above collection chain corresponds to those indicated above as related to the width of the collection surface 15.

Throat eddies are minimized by employing a smoothly curved wall to make the transition from wall 51 to wall 52 and define the throat section 45. Such a transition can be made on a radius approaching the width of collector surface 15 with the walls 51 at about from the vertical and the walls 52 at about 19 from the vertical.

in each of the embodiments it is advantageous to employ suitable seals as in the region of the collection chain 15 and provide the usual access doors for cleaning and servicing, none of which are shown. The end walls 13 and 14 have been illustrated as planar and perpendicular to the collection surface 15. While the high velocity and low impediment to flow at up stream end wall 13 imposes no significant need for modification of that wall to control flow in its vicinity, the downstream flow can be improved significantly when its end wall 14 is formed to the same general form as one of the side walls. End wall configuration becomes significant where multiple collection chambers are employed, as where a collection chamber is individual to each fiber former ll-bumer 23 combination, particularly in those modules which are arranged to deposit their fibers on a previously collected mat of fibers. Thus as the flow impediment is increased through surface 15 the benefit derived from the control of flow by collection chamber wall configuration increases.

While the proportions given for the relationship of the means discharging the primary stream, the fiber formers l1 and burners 23, to the chamber walls and collection surface 15 apply for a wide range of sizes it is to be noted that there exists a range of throat sizes and locations which will result in proper diffusion at a given flow rate. This range is about plus or minus 10 percent of the width at lower flow rates and increases to about plus or minus 20 percent as the flow rate is increased.

lt is to be appreciated that the above described collection chamber configurations lend themselves to modification and to combinations other than those shown and discussed. Accordingly, it should be understood that the disclosure is to be read as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for producing a mat of mineral fibers comprising:

discharging means for discharging mineral fibers in a primary stream directed toward a collection surface lowered below said discharging means;

said collection surface being foraminous and movable in a substantially horizontal direction.

means for developing a suction to draw gas through said collection surface to draw fibers down onto said collection surface; and

opposed side walls extending generally from said discharging means to said collection surface, upper portions of said walls and lower positions of said walls being connected by a throat region, said upper portions of said walls converging toward said throat region and defining an open mouth adjacent said discharging means, said lower portions of said walls diverging from said throat region as said lower portions approach said collection surface to define a discharge opening for said opposed walls adjacent said collection surface, said throat region having a width in a direction transverse of the direction of movement of said collection surface about 45 percent of the width of the collection surface in the transverse direction, and said throat region being spaced from said collection surface a distance of about percent of the width of the collection surface in the transverse direction.

2. Apparatus according to claim 1 wherein said side walls extend in a direction normal to said collection surface a distance of about 330 percent of the dimension of said collection surface transverse of the direction in which said surface is movable.

3. Apparatus according to claim 1 wherein said side walls define a section normal to the direction in which said collection surface is movable which is bordered by smooth curves from said open mouth to said collection surface.

4. Apparatus according to claim 1 wherein said open mouth has a width parallel to the dimension of said collection surface transverse of the direction in which said surface is movable which is about three times the width of said surface in the transverse direction.

5. Apparatus according to claim 1 wherein said lower portions of said wide walls are generally planar.

6. Apparatus according to claim 1 wherein said upper and lower portions of said side walls are generally planar and said throat section forms a smooth curved transition between said upper and lower portions.

7. Apparatus according to claim 1 including a rotating element for centrifugally forming fibers from a molten mass of material; means generating a stream of gas directed downwardly to intersect said fibers whereby said fibers are entrained in the gas as said primary stream; and an open region intermediate said primary stream and said upper portions of said walls to admit ambient cooling air with said primary stream between said walls.

8. Apparatus according to claim 1 including a plurality of discharging means spaced longitudinally above said fiber collecting surface, wherein said opposed walls extend along each side longitudinally of said collecting surface, and end walls closing the space between said opposed walls at a region beyond the most distantly spaced of said discharging means. 

1. Apparatus for producing a mat of mineral fibers comprising: discharging means for discharging mineral fibers in a primary stream directed toward a collection surface lowered below said discharging means; said collection surface being foraminous and movable in a substantially horizontal direction. means for developing a suction to draw gas through said collection surface to draw fibers down onto said collection surface; and opposed side walls extending generally from said discharging means to said collection surface, upper portions of said walls and lower positions of said walls being connected by a throat region, said upper portions of said walls converging toward said throat region and defining an open mouth adjacent said discharging means, said lower portions of said walls diverging from said throat region as said lower portions approach said collection surface to define a discharge opening for said opposed walls adjacent said collection surface, said throat region having a width in a direction transverse of the direction of movement of said collection surface about 45 percent of the width of the collection surface in the transverse direction, and said throat region being spaced from said collection surface a distance of about 150 percent of the width of the collection surface in the transverse direction.
 2. Apparatus according to claim 1 wherein said side walls extend in a direction normal to said collection surface a distance of about 330 percent of the dimension of said collection surface transverse of the direction in which said surface is movable.
 3. Apparatus according to claim 1 wherein said side walls define a section normal to the direction in which said collection surface is movable which is bordered by smooth curves from said open mouth to said collection surface.
 4. Apparatus according to claim 1 wherein said open mouth has a width parallel to the dimension of said collection surface transverse of the direction in which said surface is movable which is about three times the width of said surface in the transverse direction.
 5. Apparatus according to claim 1 wherein said lower portions of said wide walls are generally pLanar.
 6. Apparatus according to claim 1 wherein said upper and lower portions of said side walls are generally planar and said throat section forms a smooth curved transition between said upper and lower portions.
 7. Apparatus according to claim 1 including a rotating element for centrifugally forming fibers from a molten mass of material; means generating a stream of gas directed downwardly to intersect said fibers whereby said fibers are entrained in the gas as said primary stream; and an open region intermediate said primary stream and said upper portions of said walls to admit ambient cooling air with said primary stream between said walls.
 8. Apparatus according to claim 1 including a plurality of discharging means spaced longitudinally above said fiber collecting surface, wherein said opposed walls extend along each side longitudinally of said collecting surface, and end walls closing the space between said opposed walls at a region beyond the most distantly spaced of said discharging means. 